Triazine template phenol-formaldehyde resin hierarchical mesoporous carbon-silicon negative electrode composite material and preparation method

Abstract

The application belongs to the technical field of lithium ion battery negative electrode materials, and discloses a triazine template phenolic resin hierarchical mesoporous carbon silicon negative electrode composite material and a preparation method. The composite material comprises a hierarchical mesoporous carbon matrix derived from covalent triazine framework and phenolic resin synergistic pyrolysis and silicon deposited in the pores of the matrix, and the matrix has uniform mesopores and through-type hierarchical pores. The uniform mesopores are induced by the topological template effect of the microporous covalent triazine framework, the through-type hierarchical pores are constructed by in-situ chemical etching of nitrogen-containing gas generated by pyrolysis, and the nitrogen doping is left to improve the conductivity of the carbon matrix. The material provides expansion buffer space for silicon nanoparticles, promotes uniform deposition of silicon, and improves the structural stability and cycle performance of the electrode.

Description

Technical Field

[0001] This invention belongs to the field of electrode material technology, specifically relating to a triazine template phenolic resin hierarchical mesoporous silicon carbide anode composite material and its preparation method. Background Technology

[0002] Silicon-carbon composite materials, as a new generation of high-energy-density lithium-ion battery anode materials, have broad application prospects in electric vehicles, consumer electronics, and energy storage power stations. Silicon has a theoretical specific capacity of 4200 mAh / g, approximately ten times that of traditional graphite, and its abundance in the Earth's crust reaches 26.4%, making it a widely available raw material. However, silicon's volume expansion rate exceeds 300% during charge and discharge, leading to electrode structure pulverization and rapid capacity decay, severely restricting its practical application. Silicon-carbon composite materials prepared by chemical vapor deposition (CVD), by nano-sizing silicon and confining it within a hierarchical mesoporous carbon matrix, can effectively buffer volume expansion and improve conductivity, becoming the mainstream technology route for current industrial development. The pore structure of the hierarchical mesoporous carbon matrix directly determines the silicon loading, distribution uniformity, and cycle stability. Among them, phenolic resin-based porous carbon, due to its low impurities, stable structure after carbonization, and high compressive strength, is widely used as the carbon support for CVD silicon-carbon anodes. However, existing phenolic resin-based porous carbon has inherent defects such as excessively high micropore ratio, disordered pore topology, and low electronic conductivity, leading to uneven silicon deposition, carbon framework breakage, and limited high-rate performance. In existing technologies, methods that control pore structure by adding hard or soft templates require an additional etching removal step, which is complex and prone to introducing impurities; methods that use physical blending with other carbon sources for composite formation suffer from poor interfacial compatibility, leading to phase separation and making it difficult to achieve precise and synergistic control of pore structure. Summary of the Invention

[0003] To address the problems existing in the prior art, this invention provides a triazine-templated phenolic resin hierarchical mesoporous carbon silicon anode composite material and its preparation method, which effectively suppresses carbon skeleton breakage during charging and discharging and improves the structural stability of the material.

[0004] The technical solution adopted in this invention is as follows: In a first aspect, the present invention provides a triazine-templated phenolic resin hierarchical mesoporous carbon-silicon anode composite material, comprising a hierarchical mesoporous carbon matrix and silicon deposited in the pores of the matrix; the hierarchical mesoporous carbon matrix is ​​derived by the synergistic pyrolysis of a covalent triazine framework and phenolic resin, having uniform mesopores and interconnected hierarchical channels, the pore size of the uniform mesopores being 3nm-5nm; the covalent triazine framework is formed by the polymerization of cyano monomers containing triazine rings, and the hierarchical mesoporous carbon matrix contains pyrolysis residual nitrogen doping.

[0005] In conjunction with the first aspect, the present invention provides a first embodiment of the first aspect, wherein the cyano monomer containing a triazine ring comprises 2,4,6-tricyano-1,3,5-triazine and biphenyl dicyano, wherein the molar ratio of the two is (2-4):1.

[0006] In conjunction with the first aspect, the present invention provides a second embodiment of the first aspect, wherein the mass ratio of the covalent triazine framework to the phenolic resin is 1:(3-5), the surface of the covalent triazine framework particles is modified by amylation, and the covalent triazine framework and the phenolic resin are chemically bridged at the interface by a silane coupling agent.

[0007] In conjunction with the first aspect, the present invention provides a third embodiment of the first aspect, wherein the hierarchical mesoporous carbon matrix is ​​prepared by segmented pyrolysis: first, the temperature is raised to 300°C at a heating rate not exceeding 2°C / min and held at that temperature; then, the temperature is raised to 600°C at a heating rate not exceeding 1°C / min; and finally, the temperature is raised to 800°C and held at that temperature for carbonization.

[0008] In conjunction with the first aspect, the present invention provides a fourth embodiment of the first aspect, wherein the silicon is loaded by pulsed chemical vapor deposition, the pulsed chemical vapor deposition including alternating deposition, diffusion and etching stages, wherein an etching gas containing hydrogen chloride is introduced during the etching stage.

[0009] In conjunction with the first aspect, the present invention provides a fifth embodiment of the first aspect, wherein the hierarchical mesoporous carbon matrix undergoes an atmosphere switching process during pyrolysis: first, it is heated to 600°C in an inert atmosphere, then switched to a mixed atmosphere containing ammonia and heated to 800°C for holding, and finally switched back to an inert atmosphere for holding.

[0010] In conjunction with the first aspect, the present invention provides a sixth embodiment of the first aspect, wherein the surface of the composite material has an amorphous carbon coating layer with a thickness of 2nm-5nm.

[0011] In conjunction with the first aspect, the present invention provides a seventh embodiment of the first aspect, wherein the silicon filling rate inside the mesopores of the hierarchical mesoporous carbon matrix is ​​higher than the filling rate at the pore opening.

[0012] In conjunction with the second embodiment of the first aspect, the present invention provides an eighth embodiment of the first aspect, wherein the silane coupling agent is γ-aminopropyltriethoxysilane, the amination modification is achieved by ammonia reflux treatment, and the interfacial chemical bridging includes the condensation reaction between the silane coupling agent and the terminal hydroxymethyl group of the phenolic resin.

[0013] Secondly, a preparation method is also provided for preparing the aforementioned triazine-templated phenolic resin hierarchical mesoporous carbon-silicon anode composite material, characterized in that it comprises: A covalent triazine framework was composited with phenolic resin and cured to obtain a composite precursor. The composite precursor was pyrolyzed in stages under an inert atmosphere to obtain a hierarchical mesoporous carbon matrix. Silicon is deposited within the pores of a hierarchical mesoporous carbon matrix via chemical vapor deposition.

[0014] The beneficial effects of this invention are as follows: (1) The present invention forms a hierarchical mesoporous carbon matrix with uniform mesopores and interconnected hierarchical channels through the synergistic compounding and pyrolysis derivatization of covalent triazine framework and phenolic resin, providing sufficient expansion buffer space for silicon nanoparticles, effectively suppressing carbon skeleton breakage during charging and discharging, and improving the structural stability of the material. (2) The present invention utilizes nitrogen-containing gas generated by the pyrolysis of covalent triazine framework to perform in-situ chemical etching on carbon matrix, constructing through-type hierarchical channels, promoting uniform deposition of silicon in the channels, and improving process repeatability and product performance consistency. (3) The present invention achieves in-situ nitrogen doping of carbon matrix by pyrolyzing residual nitrogen atoms in a covalent triazine framework, thereby improving the electronic conductivity of carbon matrix and improving the performance of electrode under high-rate charge and discharge conditions; (4) The present invention uses covalent triazine framework particle surface amination modification and silane coupling agent interface chemical bridging to improve the interfacial compatibility between covalent triazine framework and phenolic resin, inhibit macroscopic phase separation, improve the uniformity of mesopore size distribution, and at the same time the interfacial bridging residue is transformed into silicon-oxygen-carbon ceramic phase to enhance the mechanical compressive strength of carbon skeleton. (5) The present invention uses a pulsed chemical vapor deposition process, with alternating deposition, diffusion and etching stages, combined with an axial temperature gradient, to achieve gradient filling of silicon from the inside of the mesopores to the pore openings, suppressing preferential pore blockage, and improving the uniformity of silicon filling and pore opening rate in the mesopores; by switching the atmosphere in stages during the pyrolysis process, the nitrogen doping type is controlled, the graphite nitrogen ratio is increased, and the conductivity of the carbon matrix is ​​further improved; an amorphous carbon coating layer is set on the surface of the composite material, which forms an internal and external double buffer mechanism with the internal buffer structure of the hierarchical mesoporous carbon, reducing the interfacial side reactions between silicon and electrolyte and improving cycle stability. Detailed Implementation

[0015] The present invention will be further explained below with reference to specific embodiments.

[0016] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are some embodiments of this application, but not all embodiments.

[0017] It is worth noting that, in the embodiments, the pore size distribution coefficient refers to the ratio of the half-width at half-maximum (WHWH) of the BJH mesopore size distribution curve to the average pore size, the fill rate refers to the volume ratio of silicon in a certain area of ​​the pore, and the pore open rate refers to the proportion of the effective pore volume that is not blocked to the total pore volume. The nitrogen adsorption-desorption method is used for testing. Example

[0018] This embodiment provides a triazine-templated phenolic resin hierarchical mesoporous silicon-carbon anode composite material, the preparation of which includes four main steps: composite curing of covalent triazine framework and phenolic resin, segmented pyrolysis, and chemical vapor deposition of silicon and carbon coating.

[0019] The covalent triazine framework is formed by the polymerization of 2,4,6-tricyano-1,3,5-triazine and biphenyl dicyano in a molar ratio of 3:1.

[0020] The molar ratio was chosen based on the following considerations: 2,4,6-tricyano-1,3,5-triazine has a triazine ring and three cyano groups, and its high nitrogen content makes it a microporous template source and an in-situ nitrogen source; biphenyl dicyano has a double benzene ring bridging structure, and its rigid framework can expand the pores.

[0021] A molar ratio of 3:1 ensures a moderate nitrogen release during pyrolysis. An excessively high proportion of 2,4,6-tricyano-1,3,5-triazine will lead to over-etching, while a too-low proportion will result in insufficient microporous template. The specific surface area of ​​the covalent triazine framework powder is 1200 m². 2 / g, with micropore sizes ranging from 1nm to 2nm.

[0022] The phenolic resin used is a low molecular weight linear phenolic resin with a number average molecular weight of 1000 and a softening point of 90℃. The low molecular weight facilitates penetration into the micropores of the covalent triazine framework before curing, rather than merely coating the particle surface. The mass ratio of the covalent triazine framework to the phenolic resin is 1:4. At this ratio, the covalent triazine framework can be uniformly dispersed in the phenolic resin matrix, forming a good composite structure, while simultaneously ensuring effective guidance of pore structure formation during subsequent carbonization.

[0023] Covalent triazine framework powder was added to an ethanol / water mixed solvent of phenolic resin, with a volume ratio of ethanol to water of 7:3 and a solid content controlled at 40 wt%. This mixed solvent system exhibits affinity for both the covalent triazine framework and the phenolic resin, reducing phase separation. Initial mixing was achieved by high-speed stirring for 30 min, followed by ultrasonic dispersion for 20 min to form a homogeneous slurry. The slurry was poured into a mold and heated to 80℃ for 2 h to allow solvent evaporation. Initial crosslinking was then initiated by increasing the temperature at 1℃ / min to 120℃ and holding for 1 h, followed by curing at 2℃ / min to 150℃ and holding for 2 h. This segmented curing process prevented rapid crosslinking from locking the covalent triazine framework particles in localized areas.

[0024] The cured composite precursor was placed in a tube furnace and heated to 300°C at a heating rate of 2°C / min under an argon atmosphere, and held at that temperature for 1 hour for pretreatment. The heating rate of 2°C / min, rather than a higher rate, was set at this low-temperature stage to allow the phenolic resin to further crosslink and cure fully, while the covalent triazine framework begins to depolymerize and release trace amounts of ammonia gas, pre-etching the surrounding carbon matrix to form primary pore openings.

[0025] Continue heating to 600℃ at a heating rate of 1℃ / min. The lower heating rate is used in this intermediate temperature stage because the phenolic resin undergoes violent pyrolysis at this stage, generating a large number of free radicals. The covalent triazine framework micropores act as topological constraint templates, restricting the disordered shrinkage of the carbon matrix and inducing the formation of uniform mesopores.

[0026] The temperature was then increased to 800℃ at a rate of 3℃ / min and held for 2 hours for carbonization. The heating rate was restored to 3℃ / min during the high-temperature stage because the covalent triazine framework was completely decomposed, releasing nitrogen-containing gas to perform in-situ chemical etching on the carbon matrix, constructing a through-type hierarchical pore structure, while residual nitrogen atoms were embedded in the carbon framework. After carbonization, the matrix was cooled to room temperature in the furnace to obtain a hierarchical mesoporous carbon matrix, which was then pulverized by airflow to a D50 of 8 μm.

[0027] A hierarchical mesoporous carbon matrix was placed in a chemical vapor deposition (CVD) furnace, and a mixture of silane and argon gas was introduced. The silane volume fraction was 5%, the gas flow rate was 200 sccm, the deposition temperature was 560℃, and the deposition time was 2 h. Then, the temperature was raised to 400℃, and acetylene gas was introduced for carbon coating. The acetylene volume fraction was 5%, and the coating time was 30 min. The silane volume fraction was controlled at 5% to balance the deposition rate and pore penetration depth; too high a concentration would lead to rapid pore blockage, while too low a concentration would result in insufficient deposition efficiency. The deposition temperature of 560℃ is within the optimal window for silane thermal decomposition, ensuring sufficient decomposition of silane and the formation of nanoscale amorphous silicon particles, avoiding excessive grain growth. A silicon-carbon composite material was obtained, in which the silicon mass content was 47.1 wt%.

[0028] During the curing stage, the phenolic resin undergoes a cross-linking reaction to form a three-dimensional network structure, in which covalent triazine framework particles are uniformly dispersed. During the pyrolysis stage, the microporous structure of the covalent triazine framework acts as a topological template, constraining the disordered shrinkage of the phenolic resin during pyrolysis and inducing the formation of uniform mesopores with a pore size of 3nm-5nm.

[0029] Simultaneously, the triazine rings and cyano groups in the covalent triazine framework undergo pyrolysis above 600°C, releasing nitrogen-containing gases such as ammonia and hydrogen cyanide. These gases react with the carbon matrix in situ through chemical etching, constructing interconnected hierarchical channels. The nitrogen atoms remaining from the pyrolysis embed into the carbon framework, forming pyridine nitrogen, pyrrole nitrogen, and graphitic nitrogen, thus improving the electronic conductivity of the carbon matrix. During the chemical vapor deposition stage, silanes undergo thermal decomposition within the carbon matrix channels, and silicon atoms are deposited on the mesoporous inner walls, forming a silicon / carbon composite structure.

[0030] Nitrogen adsorption-desorption tests were performed on the hierarchical mesoporous carbon matrix, and the results showed that its specific surface area was 850 m². 2 / g, pore volume 1.2cm 3 The pore size is concentrated at 3.8 nm, with mesopores accounting for 65%, micropores for 15%, and macropores for 20%, and the pore size distribution coefficient is 0.28. The conductivity was measured using the four-probe method, and the result was 32 S / m.

[0031] X-ray photoelectron spectroscopy analysis showed a nitrogen content of 8.5 wt%. Electrochemical tests were conducted on button cells made from the composite material. The initial reversible specific capacity at 0.1C rate was 1850 mAh / g, and the capacity retention after 100 cycles at 1C rate was 88%. Example

[0032] This embodiment provides a triazine-template hierarchical mesoporous carbon-silicon anode composite material with interfacial chemical bridging. Its preparation includes five main steps: covalent triazine framework surface amination modification, composite curing with phenolic resin containing silane coupling agent, segmented pyrolysis, and chemical vapor deposition of silicon and carbon coating.

[0033] The covalent triazine framework monomers and their proportions were the same as in Example 1. Before compounding the covalent triazine framework powder with the phenolic resin, the covalent triazine framework particles were first subjected to surface amination modification: the covalent triazine framework powder was placed in a mixture of ammonia and ethanol at a volume ratio of 1:1, refluxed at 60°C for 4 hours, followed by centrifugation, washing, and vacuum drying to obtain a surface-aminated covalent triazine framework. The ammonia reflux treatment temperature was set at 60°C rather than a higher temperature to allow ammonia molecules to attack the cyano residues or triazine ring edges on the surface of the covalent triazine framework under mild conditions, introducing primary amino and imino groups, while avoiding the destruction of the covalent triazine framework skeleton due to high temperatures.

[0034] The same low molecular weight linear phenolic resin as in Example 1 was used, and γ-aminopropyltriethoxysilane was added to the phenolic resin solution at a concentration of 1.0 wt% of the phenolic resin mass. This addition of 1.0 wt% was controlled to ensure effective bridging at the interface without introducing excessive non-carbon impurities. The surface-aminated covalent triazine framework was added to the phenolic resin solution containing γ-aminopropyltriethoxysilane, stirred at high speed for 30 min, and ultrasonically dispersed for 20 min. The mixed slurry was poured into a mold and held at 80°C for 2 h, then heated to 120°C at a rate of 1°C / min and held for 1 h, and finally heated to 150°C at a rate of 2°C / min and held for 2 h to complete curing. A mild pressure of 1.0 MPa was applied during curing. This pressure was set to promote the full penetration of the phenolic resin into the gaps and surface micropores of the covalent triazine framework, forming an interpenetrating network structure rather than a simple island structure.

[0035] The pyrolysis and chemical vapor deposition processes, and the carbon coating are the same as in Example 1.

[0036] Surface amination modification introduces primary amino and imino groups onto the surface of the covalent triazine framework. These groups form hydrogen bonds with the phenolic hydroxyl groups in the phenolic resin and undergo condensation reactions with the hydroxymethyl groups at the ends of the phenolic resin during curing, forming carbon-nitrogen covalent bridges. One end of the γ-aminopropyltriethoxysilane hydrolyzes and binds to the surface of the covalent triazine framework, while the other end reacts with the hydroxyl groups of the phenolic resin, forming a flexible siloxane bridging segment. This bridging segment transforms into silicon-oxygen-carbon bonds during pyrolysis, enhancing interfacial bonding. Simultaneously, the residual silicon oxide serves as a heterogeneous nucleation site, promoting the uniform distribution of silicon within the pores.

[0037] Nitrogen adsorption-desorption tests were performed on the hierarchical mesoporous carbon matrix. The mesopore size was concentrated at 3.9 nm, with a mesopore ratio of 68% and a pore size distribution coefficient of 0.12, which was significantly lower than 0.28 in Example 1. The compressive strength of the carbon matrix was tested using a universal testing machine, and the result was 26 MPa. The electrical conductivity was tested and the result was 35 S / m. The capacity retention after 100 cycles at 1C was 85%. Example

[0038] This embodiment provides a triazine-templated hierarchical mesoporous silicon-carbon anode composite material based on pulsed chemical vapor deposition. Its preparation includes four main steps: composite curing of covalent triazine framework and phenolic resin, segmented pyrolysis, and pulsed chemical vapor deposition of silicon and carbon coating.

[0039] The preparation of the hierarchical mesoporous carbon matrix was the same as in Example 2, using a covalent triazine framework / phenolic resin composite precursor that was surface-aminated and bridged by γ-aminopropyltriethoxysilane, which was obtained by staged pyrolysis and air jet milling.

[0040] Chemical vapor deposition (CVD) was performed using a pulsed process in a fluidized bed reactor with an axial temperature gradient established. The temperature at the silane inlet at the bottom of the reactor was set at 450°C, and the temperature at the top was set at 510°C. This axial temperature gradient was designed to allow silane to undergo initial decomposition in the cooler lower region, preferentially depositing inside the channels. Unreacted silane then rises to the higher temperature region to complete its final decomposition, replenishing the outer layer and thus promoting a gradient distribution of silicon from the inside out.

[0041] Pulsed chemical vapor deposition consists of 100 pulse cycles, each containing three stages. During the deposition stage, a mixture of silane and argon is introduced, with a silane volume fraction of 8%, a gas flow rate of 250 sccm, a duration of 60 s, and a temperature maintained at 580 °C.

[0042] The silane volume fraction of 8% is higher than 5% in Example 1 because the diffusion and etching stages in the pulsed process remove some of the deposits, requiring a higher instantaneous deposition rate to achieve a comparable silicon content within the same total time. During the diffusion stage, silane is shut off, and only argon gas is introduced at a flow rate of 200 sccm for 120 s. This duration of 120 s is set to utilize the concentration difference inside and outside the pores to allow residual silane to diffuse sufficiently into the depths of the pores, while simultaneously expelling the byproduct hydrogen gas.

[0043] During the etching stage, a mixture of hydrogen chloride and argon gas was introduced, with a hydrogen chloride volume fraction of 2%, a flow rate of 80 sccm, and a duration of 20 s. Afterward, the temperature was raised to 590℃, and acetylene gas was introduced for carbon coating, with an acetylene volume fraction of 25%, for a coating time of 1.5 h. The hydrogen chloride volume fraction was controlled at 2% to selectively etch the excessively thick silicon deposit at the orifice, reopening the orifice, while the silicon inside the channel, protected by the carbon walls and with a thinner deposition, suffered less loss. If the concentration was too high, the internal silicon loss would increase; if it was too low, the etching effect at the orifice would be insufficient.

[0044] During the deposition stage, silanes undergo thermal decomposition within the hierarchical mesoporous carbon matrix channels, depositing silicon atoms onto the inner walls of the mesopores. During the diffusion stage, residual silanes diffuse deeper into the channels, while hydrogen gas, a byproduct, is expelled. In the etching stage, hydrogen chloride selectively etches away any excessively thick silicon deposits at the pore openings, reopening them. Through multiple pulse cycles, silicon gradually fills the channels from the interior to the exterior, creating a gradient distribution where the internal filling rate of the mesopores is higher than that at the pore openings.

[0045] The silicon content in the composite material is 48.9 wt%. Linear scanning analysis of the composite material cross-section was performed using scanning electron microscopy combined with energy dispersive spectroscopy. Along the radial direction of the mesopores from the interior to the pore opening, the silicon atomic percentage gradually decreased from approximately 65% ​​at the interior to approximately 35% at the pore opening, confirming that the silicon filling rate inside the mesopores is higher than at the pore opening. The pore openness was measured to be 72% using a nitrogen adsorption-desorption method. The test principle is to calculate the effective open pore volume percentage by comparing the pore volume difference between the adsorption and desorption branches. The initial reversible specific capacity at 0.1C rate was 1920 mAh / g, and the capacity retention after 100 cycles at 1C rate was 88%. Example

[0046] This embodiment provides a triazine template hierarchical mesoporous silicon-carbon anode composite material based on segmented atmosphere switching. Its preparation includes four main steps: composite curing of covalent triazine framework and phenolic resin, segmented atmosphere switching pyrolysis, and chemical vapor deposition of silicon and carbon coating.

[0047] The composite and curing process of the covalent triazine framework with phenolic resin, as well as the carbon coating, are the same as in Example 1.

[0048] The pyrolysis process employs a segmented atmosphere switching method: the composite precursor is placed in a tube furnace and heated to 300°C at a heating rate of 2°C / min under an argon atmosphere, and held for 1 hour; then heated to 600°C at a heating rate of 1°C / min. Subsequently, the atmosphere is switched to a mixed atmosphere of ammonia and argon, with an ammonia gas fraction of 10%, and heated to 800°C at a heating rate of 2°C / min, and held for 1 hour.

[0049] The ammonia gas fraction was set to 10% to provide sufficient nitrogen source to promote nitrogen formation in graphite, while avoiding excessive nitrogen doping that could lead to carbon structural defects due to excessive concentration. The atmosphere was then switched back to pure argon and held at that temperature for 1 hour. Finally, the atmosphere was switched back to argon to prevent excessive etching of the carbon matrix caused by continuous ammonia atmosphere at 800℃. After carbonization, the furnace was cooled to room temperature.

[0050] The chemical vapor deposition process and carbon coating are the same as in Example 1.

[0051] Below 600℃, phenolic resin undergoes pyrolytic crosslinking under an argon atmosphere, causing the covalent triazine framework to decompose and release nitrogen-containing gases. Between 600℃ and 800℃, the atmosphere is switched to an ammonia-mixed atmosphere. The external ammonia reacts with the carbon matrix, promoting the conversion of pyridine nitrogen to graphitic nitrogen and increasing the proportion of graphitic nitrogen. The sp² hybridization structure of graphitic nitrogen contributes most significantly to the improvement of the electronic conductivity of the carbon framework. Finally, the atmosphere is switched back to argon to avoid excessive nitrogen doping that could lead to structural defects in the carbon structure.

[0052] The conductivity was measured using the four-probe method, yielding a result of 68 S / m. X-ray photoelectron spectroscopy analysis showed a nitrogen content of 10.2 wt%, with graphitic nitrogen accounting for 42%, pyridine nitrogen for 35%, and pyrrole nitrogen for 23%. The initial reversible specific capacity at 0.1C was 1900 mAh / g, the discharge specific capacity at 5C was 82% of the capacity at 1C, and the capacity retention after 100 cycles at 1C was 80%. Example

[0053] This embodiment provides a triazine template hierarchical mesoporous silicon carbide anode composite material with surface coating. Its preparation includes four main steps: composite curing of covalent triazine framework and phenolic resin, segmented pyrolysis, pulsed chemical vapor deposition of silicon, and surface coating.

[0054] The matrix of the silicon-carbon composite material is the same as in Example 3. After loading silicon via pulsed chemical vapor deposition, the composite material is transferred to a chemical vapor deposition reactor. A mixture of acetylene and argon gas is introduced at 400°C, with an acetylene volume fraction of 5%, and the treatment time is 30 minutes. The temperature is set at 400°C to allow acetylene to undergo pyrolysis and polymerization to form an amorphous carbon coating layer. This temperature is lower than the recrystallization temperature of silicon, which can prevent the growth of already deposited silicon grains and isolate oxygen to prevent silicon oxidation. The combination of a 5% acetylene volume fraction and a treatment time of 30 minutes allows the coating layer thickness to be controlled within the range of 2nm-5nm. Too thick a coating layer would hinder lithium-ion transport, while too thin a coating layer would result in incomplete coating.

[0055] A 3 nm thick amorphous carbon coating layer is formed on the surface of the composite material. This coating layer acts as an artificial solid electrolyte interface film, buffering the mechanical stress during silicon expansion, reducing direct contact between silicon and the electrolyte, and suppressing interfacial side reactions. This coating layer, together with the internal buffer structure of the hierarchical mesoporous carbon matrix, forms a dual buffering mechanism, maintaining lithium-ion transport channels while improving cycle stability.

[0056] Transmission electron microscopy revealed a uniform coating layer approximately 3 nm thick on the surface of the composite material. The capacity retention was 92% after 100 cycles at 1C magnification. The capacity retention was 85% after 50 cycles at 55°C. Example

[0057] This embodiment provides two triazine-templated phenolic resin hierarchical mesoporous silicon carbide anode composite materials with different monomer ratios. The preparation steps are the same as in Example 1, except that the ratio of covalent triazine framework monomers is different.

[0058] In one implementation, the molar ratio of 2,4,6-tricyano-1,3,5-triazine to biphenyl dicyano is 2:1. At this ratio, the proportion of biphenyl dicyano is relatively high, resulting in a more pronounced effect of rigid bridging structure in expanding the pores. The resulting hierarchical mesoporous carbon matrix has a mesopore size concentrated at 4.5 nm, with a mesopore ratio of 60%, making it suitable for applications requiring larger pore sizes to buffer silicon expansion.

[0059] In other embodiments, the molar ratio of 2,4,6-tricyano-1,3,5-triazine to biphenyl dicyano is 4:1. At this ratio, the triazine ring content is higher, and the nitrogen doping amount increases after pyrolysis. The nitrogen content of the hierarchical mesoporous carbon matrix is ​​12 wt%, and the electrical conductivity is 45 S / m. However, the mesopore size is concentrated at 3.2 nm, and the proportion of micropores increases slightly.

[0060] The sample with a molar ratio of 2:1 has a mesopore size of 4.5 nm, a specific surface area of ​​780 m² / g, an electrical conductivity of 28 S / m, and an initial reversible specific capacity of 1800 mAh / g. The sample with a molar ratio of 4:1 has a mesopore size of 3.2 nm, a specific surface area of ​​920 m² / g, an electrical conductivity of 45 S / m, and an initial reversible specific capacity of 1880 mAh / g. Example

[0061] This embodiment provides a method for preparing a triazine-templated phenolic resin hierarchical mesoporous silicon-carbon anode composite material, including four main steps: composite curing of covalent triazine framework and phenolic resin, segmented pyrolysis, chemical vapor deposition, and carbon coating.

[0062] Step 1: The covalent triazine framework is composited with phenolic resin and cured to obtain the composite precursor. The covalent triazine framework is formed by the polymerization of cyano monomers containing triazine rings, and the phenolic resin is a low molecular weight linear phenolic resin. The covalent triazine framework powder is added to the phenolic resin solution, and a uniform slurry is formed by high-speed stirring and ultrasonic dispersion. The slurry is then cured by staged heating to obtain the composite precursor.

[0063] As one implementation method, the surface of the covalent triazine framework particles can be pre-aminated, and a silane coupling agent can be added to the phenolic resin solution to form interfacial chemical bridges. A mild pressure of 0.5 MPa to 2 MPa can be applied during the curing process. This pressure range is set to promote sufficient penetration of the phenolic resin into the gaps between the covalent triazine framework particles, forming an interpenetrating network structure. Too low a pressure will result in insufficient penetration, while too high a pressure will cause the covalent triazine framework skeleton to be damaged by pressure.

[0064] Step 2: The composite precursor is pyrolyzed in stages under an inert atmosphere to obtain a hierarchical mesoporous carbon matrix. The staged pyrolysis includes: heating to 300℃ at a rate not exceeding 2℃ / min and holding at that temperature; heating to 600℃ at a rate not exceeding 1℃ / min; and finally heating to 800℃ and holding at that temperature for carbonization. The heating rate of no more than 2℃ / min at the 300℃ stage is used to ensure sufficient cross-linking of the phenolic resin and release of volatile substances, while the covalent triazine framework begins to decompose, releasing trace amounts of nitrogen-containing gas for pre-etching. A lower heating rate of no more than 1℃ / min is used at the 600℃ stage because the vigorous pyrolysis of the phenolic resin at this stage generates a large number of free radicals, requiring the micropores of the covalent triazine framework as a topological constraint template to induce the formation of uniform mesopores. The 800℃ stage completely decomposes the covalent triazine framework, releasing nitrogen-containing gas for in-situ chemical etching and constructing interconnected hierarchical channels.

[0065] In one implementation method, after heating to 600°C, the atmosphere can be switched to a mixed atmosphere containing ammonia and the temperature can be further increased to 800°C for holding. Finally, the atmosphere can be switched back to an inert atmosphere for holding. The purpose of switching the atmosphere is to control the nitrogen doping type and increase the nitrogen ratio in the graphite.

[0066] Step 3: Silicon is deposited within the pores of the hierarchical mesoporous carbon matrix via chemical vapor deposition (CVD). As one implementation method, CVD can be performed using a continuous deposition process, with a silane volume fraction of 5%-10% and a deposition temperature of 550℃-600℃. The 5%-10% silane volume fraction range is set to balance the deposition rate and pore penetration depth, and the 550℃-600℃ deposition temperature falls within the suitable window for silane thermal decomposition.

[0067] In other embodiments, chemical vapor deposition can employ a pulsed process, including alternating deposition, diffusion, and etching stages. During the etching stage, an etching gas containing hydrogen chloride is introduced, establishing an axial temperature gradient within the reactor. The purpose of introducing hydrogen chloride during the etching stage in a pulsed process is to selectively remove excessively thick deposits at the orifice, maintaining the orifice's openness.

[0068] Step 4: Optionally, after chemical vapor deposition, the composite material is surface coated to form an amorphous carbon coating layer with a thickness of 2nm-5nm on the surface of the composite material. The purpose of this coating treatment is to form an artificial solid electrolyte interface film and reduce interfacial side reactions.

[0069] The three batches of composite materials prepared according to the above method all had mesopore sizes concentrated in the range of 3.5nm-4.2nm, pore size distribution coefficients all below 0.30, electrical conductivity ranging from 30S / m to 70S / m, silicon content ranging from 45wt% to 50wt%, and capacity retention rates ranging from 78% to 92% after 100 cycles at 1C rate, with batch-to-batch performance deviations of less than 8%.

[0070] Comparative Example 1: Pure Phenolic Resin-Based Porous Silicon Carbon Anode Composite Material The covalent triazine framework in Example 1 was replaced with an equal mass of phenolic resin, i.e., only phenolic resin was used as the carbon precursor. A hierarchical mesoporous carbon matrix was prepared using the same curing and pyrolysis processes, and then silicon was loaded using the same continuous chemical vapor deposition process. The resulting hierarchical mesoporous carbon matrix had a wide pore size distribution, no uniform mesoporous peaks, a micropore ratio of 55%, and a conductivity of 12 S / m. The capacity retention after 100 cycles at 1C was 55%.

[0071] Comparative Example 2: Covalent triazine framework / phenolic resin composite silicon anode material without interface modification The same covalent triazine framework and phenolic resin as in Example 1 were used, but without surface amination modification or the addition of silane coupling agents. The mixture was directly cured after high-speed stirring and ultrasonic dispersion. Macroscopic agglomeration occurred after curing. After pyrolysis, the hierarchical mesoporous carbon matrix exhibited a pore size distribution coefficient of 0.38, a compressive strength of 9 MPa, and an electrical conductivity of 25 S / m. The capacity retention after 100 cycles at 1C was 68%.

[0072] It is worth noting that the comparison between the above comparative examples and Examples 1 and 2 shows that simple physical blending of the covalent triazine framework and phenolic resin cannot achieve a uniform mesoporous structure and high mechanical strength, while interfacial chemical bridging is necessary to realize the synergistic effect of the two. Those skilled in the art should understand that the specific parameters in the above embodiments can be reasonably adjusted within the scope defined by this invention without departing from the core concept of this invention.

[0073] This invention is not limited to the optional embodiments described above, and anyone can derive other various forms of products based on the inspiration of this invention. The specific embodiments described above should not be construed as limiting the scope of protection of this invention; the scope of protection of this invention should be determined by the claims, and the specification can be used to interpret the claims.

Claims

1. A triazine-templated phenolic resin hierarchical mesoporous carbon-silicon anode composite material, characterized in that, The product includes a hierarchical mesoporous carbon matrix and silicon deposited within the pores of the matrix. The hierarchical mesoporous carbon matrix is ​​derived from the synergistic pyrolysis of a covalent triazine framework and phenolic resin, and has uniform mesopores and interconnected hierarchical channels. The pore size of the uniform mesopores is 3nm-5nm. The covalent triazine framework is formed by the polymerization of cyano monomers containing triazine rings, and the hierarchical mesoporous carbon matrix contains residual nitrogen doping from pyrolysis.

2. The triazine-templated phenolic resin hierarchical mesoporous carbon-silicon anode composite material according to claim 1, characterized in that, The triazine-containing cyano monomers include 2,4,6-tricyano-1,3,5-triazine and biphenyl dicyano, with a molar ratio of (2-4):

1.

3. The triazine-templated phenolic resin hierarchical mesoporous carbon-silicon anode composite material according to claim 1, characterized in that, The mass ratio of the covalent triazine framework to the phenolic resin is 1:(3-5). The surface of the covalent triazine framework particles is modified by amylation, and the covalent triazine framework and the phenolic resin are chemically bridged at the interface by a silane coupling agent.

4. The triazine-templated phenolic resin hierarchical mesoporous carbon-silicon anode composite material according to claim 1, characterized in that, The hierarchical mesoporous carbon matrix is ​​prepared by staged pyrolysis: first, the temperature is raised to 300°C at a heating rate not exceeding 2°C / min and held at that temperature; then, the temperature is raised to 600°C at a heating rate not exceeding 1°C / min; and finally, the temperature is raised to 800°C and held at that temperature for carbonization.

5. The triazine-templated phenolic resin hierarchical mesoporous carbon-silicon anode composite material according to claim 1, characterized in that, The silicon is loaded via pulsed chemical vapor deposition, which includes alternating deposition, diffusion, and etching stages, with the etching stage introducing an etching gas containing hydrogen chloride.

6. The triazine-templated phenolic resin hierarchical mesoporous carbon-silicon anode composite material according to claim 4, characterized in that, The hierarchical mesoporous carbon matrix undergoes atmosphere switching during pyrolysis: first, it is heated to 600°C in an inert atmosphere, then switched to a mixed atmosphere containing ammonia and heated to 800°C for holding, and finally switched back to an inert atmosphere for holding.

7. The triazine-templated phenolic resin hierarchical mesoporous carbon-silicon anode composite material according to claim 1, characterized in that, The surface of the composite material has an amorphous carbon coating layer with a thickness of 2nm-5nm.

8. The triazine-templated phenolic resin hierarchical mesoporous carbon-silicon anode composite material according to claim 1, characterized in that, The filling rate of silicon inside the mesopores of a hierarchical mesoporous carbon matrix is ​​higher than that at the pore openings.

9. The triazine-templated phenolic resin hierarchical mesoporous carbon silicon anode composite material according to claim 3, characterized in that, The silane coupling agent is γ-aminopropyltriethoxysilane, and the amination modification is achieved by reflux treatment with ammonia. The interfacial chemical bridging includes the condensation reaction between the silane coupling agent and the terminal hydroxymethyl group of the phenolic resin.

10. A preparation method for preparing the triazine-templated phenolic resin hierarchical mesoporous carbon silicon anode composite material according to claim 1, characterized in that, include: A covalent triazine framework was composited with phenolic resin and cured to obtain a composite precursor. The composite precursor was pyrolyzed in stages under an inert atmosphere to obtain a hierarchical mesoporous carbon matrix. Silicon is deposited within the pores of a hierarchical mesoporous carbon matrix via chemical vapor deposition.